Combustion devices of gas turbines are known to comprise a plurality of mixing devices, wherein a fluid (e.g., air) containing oxygen is supplied and is mixed with a fuel injected via lances projecting thereinto, to form a mixture.
The mixture passes through the mixing devices and enters a combustion chamber connected downstream of the mixing devices. Combustion of the mixture occurs in the combustion chamber.
The mixing devices are generally identical to each other. For instance, the mixing devices each have a conical body with lateral slots for the air entrance and a lance located axially in the conical body for the fuel injection. In addition, nozzles are often also located at the conical body.
During operation, the fuel is injected via the lance and/or nozzles into the conical body, and it is mixed with the air entering via the slots to form the mixture that then enters the combustion chamber and burns.
During combustion, pressure pulsations are generated. These pressure pulsations may be detrimental for the longevity of the combustion device and must be damped.
For this reason, the mixing devices connected to one combustion chamber are usually grouped in groups of four or more mixing devices. In each group, one of the mixing devices is operated at a temperature that is lower than the operating temperature of the other mixing devices of the same group (in practice, the amount of fuel supplied is lower than the amount of fuel supplied to the other mixing devices).
This operating mode causes the pressure oscillations that the mixing devices naturally generate during operation to be compensated for and balanced, such that no or low pressure pulsations emerge from the combustion device.
Nevertheless, since the temperature in the combustion chamber is not uniform (e.g., there are colder areas fed by leaner mixing devices and hotter areas fed by richer mixing devices), the temperature, for example, at the first stages of the turbine is also not uniform. This causes stress to both the combustion device (e.g., its combustion chamber) and the rotor blades in front of it, where such stress may lead to a reduced lifetime of the affected components.
In addition, in some operating conditions, the control of the fuel in the different mixing devices of the same group can be difficult. For example, fuel adjustment of the mixing devices that must receive a reduced amount of fuel is difficult at different operating loads.